In a magnetic resonance system, also known as magnetic resonance tomography system or magnetic resonance installation, in order to produce magnetic resonance recordings the body to be examined is typically exposed to a relatively high basic magnetic field, for example of 1.5, 3 or 7 tesla, with the aid of a basic field magnet system. In addition, a magnetic field gradient is applied with the aid of a gradient system. Using a high-frequency transmit system, high-frequency excitation signals (HF signals) are then emitted via suitable antenna devices, which should result in the nuclear spin of particular atoms resonantly excited by this high-frequency field being tilted by a defined flip angle compared to the magnetic field lines of the basic magnetic field.
When the nuclear spins are relaxed, high-frequency signals known as magnetic resonance signals are emitted and are received by a high-frequency receive system via suitable receiving antennas and then further processed. From the raw data thereby acquired, the desired image data can finally be reconstructed.
For a particular measurement, a particular pulse sequence then has to be emitted, which consists of a series of high-frequency pulses, in particular excitation pulses and refocusing pulses, as well as gradient pulses to be emitted suitably coordinated therewith in various spatial directions. Temporally adapted thereto, readout windows for the high-frequency receive system must be set, during which the induced magnetic resonance signals are acquired. Of particular importance here for the imaging is in particular the timing within the sequence, that is, the temporal intervals at which pulses follow one another. FIG. 1 shows an example of such a pulse sequence.
An MR system has at least one control computer, on which the cited sequence is executed. Furthermore, an MR system comprises a digital control device, which receives control data from the control computer comprising the pulse sequence and accordingly applies pulses, such as, for instance, gradient pulses, HF pulses etc., with which the imaging process is carried out.
FIG. 2 shows a conventional arrangement of an MR system with a control computer and a digital control device activated by the control computer.
A standard computer is readily used as a control computer and image reconstruction computer. It is particularly advantageous here, for cost reasons, to take an “off-the-shelf” computer that is unmodified as far as possible, and to allow the MR-specific software to run on it (in particular the software for controlling the measurement, in other words the “sequence”). Both this and also the receipt of the MR raw data requires a real-time operating system, since, in each case, it is necessary to communicate with hardware specific to the MR system and the data buffers realized there have a restricted size and in particular the data for activating the MR system-specific hardware is to be transmitted over a very short period of time.
The digital control device specific to the MR system realizes the execution of these instructions for the sequence. Since in this regard an extremely time-critical and jitter-free synchronization of the various subsystems or their activities (gradient, TY, RX, periphery) is important, this process cannot be realized solely with software, but instead requires a cycle-precise implementation with the aid of FPGAs, for instance.
Part of the hardware specific to the MR system is typically accommodated at least in parts in the control computer, in order to be able to supply the digital control device with very short communication times with the instructions generated from the sequence. It would be simpler and more cost-effective to use external communication interfaces, which involve a home computer, for instance USB interfaces or Ethernet interfaces.
Unfortunately these external OTS interfaces (OTS=off the shelf=designed as a standard product) cannot be used or only very ineffectively, since the data generally has to be passed through comprehensive software layers of the operating system and/or non-influenceable hardware protocols and a time-critical application of control commands is therefore not possible precisely. In such a case, the connection via the computer-internal buses, for instance PCIe bus systems, is therefore used, for which separate drivers can be written and the timing is therefore kept sufficiently under control. The major disadvantage here is that in this way computer interfaces are used, which are only accessible internally, i.e. for an installation of such an interface the computer has to be opened and additional hardware fitted. A simple connection of the MR-specific hardware using cables or plugs to an existing standard-external interface would be ideal, like for instance USB or Ethernet, without needing to open and therefore modify the computer.
The synchronization of the afore-cited system components or subsystems and the associated device types within the required accuracy range places high demands on the controller and thus also on the temporally correct application and transmission of the pulse sequence by the control computer of the MR system to the control device.
DE 102006052437 A1 and DE 102008017819 B3 each show a design of an MR control system; DE 102007058872 A1, US 20090137898 A1, US 20160174928 A1 each show devices for transmitting data in an MR system.